1. Field of the Invention
This invention relates to storing and using metadata in multiple storage locations and more particularly relates to copy repair of global metadata stored in multiple storage locations.
2. Description of the Related Art
The explosion of data created by e-business is making storage a strategic investment priority for companies of all sizes. As storage takes precedence, two major concerns have emerged: business continuity and business efficiency. Business continuity requires storage that supports data availability so employees, customers and trading partners can access data continuously through reliable, disaster-tolerant systems. Business efficiency, where storage is concerned, is the need for investment protection, reduced total cost of ownership and high performance and manageability.
In order to maintain the large amounts of data created and collected, storage area networks (SANs) have been developed. The Storage Network Industry Association (SNIA) defines SAN as a network whose primary purpose is the transfer of data between computer systems and storage elements. A SAN may comprise a communication infrastructure, which provides physical connections; and a management layer, which organizes the connections, storage elements, and computer systems so that data transfer is secure and robust. A SAN may also be a storage subsystem comprising storage elements, storage devices, computer systems, and/or appliances, plus all control software, communicating over a network.
Commonly, a storage area network includes a plurality of storage devices, such as tape drives or hard disk drives, connected with a storage or disk controller. The disk controller is generally a server that is configured to process read/write requests from hosts or client machines. The hosts may be running a variety of operating systems such as Windows, Linux, UNIX, AIX, etc. In large computing environments, the storage area network is an ideal solution for providing large amounts of storage and scalable server or storage controller performance.
Typically, in a storage area network environment, a host requests data from the disk controller. The disk controller then retrieves the data from the particular storage device that contains the requested data, often referred to as a home location. The disk controller then sends the data to the host. If the host modifies the data, the data is sent back to the disk controller which returns the modified data to the home location. Typically, the host awaits a response from the disk controller indicating the read or write operation has completed.
The disk controller may also provide functions such as the ability to access devices by heterogeneous servers, a data cache, data availability features such as various RAID implementations, scalability, virtualization of devices, and replication services.
In storage subsystems, large amounts of critical data known as Global Metadata (GD) maintain important subsystem configuration data. The subsystem configuration data may include file system configuration data, space usage quotas, access control lists, and extended attributes. To ensure that GD is highly available, the disk controller store three redundant copies on chosen RAID arrays. The three redundant copies are known as primary, secondary, and tertiary copies.
When a track of the GD becomes unusable the disk controller is currently configured to discard the entire copy of the metadata, and use an alternative usable copy of the GD to copy onto a target RAID array. Unfortunately, a major disadvantage of discarding an entire copy of the GD is that multiple copies of GD may be found unusable or unreadable thereby causing the disk controller to discard all copies of the GD and subsequently lose all access to the GD. Additionally, other problems include unnecessary churn of GD RAID arrays and possible loss of redundancy during the initial boot up of the storage subsystem because new arrays are not allowed to be copied at boot up time.
From the foregoing discussion, it should be apparent that a need exists for an apparatus, system, and method that prevent discarding of entire copies of global metadata. Beneficially, such an apparatus, system, and method would mark a track as unusable and find a usable copy of that track, or mark the track as invalid so that the owner of the track will perform a recovery action, and perform one or the other without discarding an entire copy of the GD.